JP3965567B2 - battery - Google Patents

Description

【００５１】
【化４】

【００５２】
また、電解質塩には、このようなＭ−Ｏ結合を有するリチウム塩に加えて、他のリチウム塩を混合して用いることが好ましい。保存特性などの電池特性をより向上させることができるからである。他のリチウム塩としては、例えば、ＬｉＡｓＦ₆ 、ＬｉＰＦ₆ 、ＬｉＢＦ₄ 、ＬｉＣｌＯ₄ 、ＬｉＢ（Ｃ₆ Ｈ₅ ）₄ 、ＬｉＣＨ₃ ＳＯ₃ 、ＬｉＣＦ₃ ＳＯ₃ 、ＬｉＮ（ＣＦ₃ ＳＯ₂ ）₂ 、ＬｉＮ（Ｃ₂ Ｆ₅ ＳＯ₂ ）₂ 、ＬｉＮ（Ｃ₄ Ｆ₉ ＳＯ₂ ）（ＣＦ₃ ＳＯ₂ ）、ＬｉＣ（ＣＦ₃ ＳＯ₂ ）₃ 、ＬｉＡｌＣｌ₄ 、ＬｉＳｉＦ₆ 、ＬｉＣｌあるいはＬｉＢｒが挙げられ、これらのいずれか１種または２種以上を混合して用いてもよい。
【００５３】
中でも、ＬｉＰＦ₆ 、ＬｉＢＦ₄ 、ＬｉＣｌＯ₄ 、ＬｉＮ（ＣＦ₃ ＳＯ₂ ）₂ ，ＬｉＮ（Ｃ₂ Ｆ₅ ＳＯ₂ ）₂ およびＬｉＣ（ＣＦ₃ ＳＯ₂ ）₃ は、より高い効果を得ることができると共に、高い導電率を得ることができるので好ましい。
【００５４】
電解質塩の含有量（濃度）は溶媒に対して０．４ｍｏｌ／ｌ以上３．０ｍｏｌ／ｌ以下の範囲内であることが好ましい。この範囲外ではイオン伝導度の極端な低下により十分な電池特性が得られなくなる虞があるからである。そのうち、Ｍ−Ｏ結合を有するリチウム塩の含有量は溶媒に対して０．０１ｍｏｌ／ｌ以上２．０ｍｏｌ／ｌ以下の範囲内であることが好ましい。この範囲内においてより高い効果を得ることができるからである。
【００５５】
なお、電解液に代えて、高分子化合物に電解液を保持させたゲル状の電解質を用いてもよい。ゲル状の電解質は、イオン伝導度が室温で１ｍＳ／ｃｍ以上であるものであればよく、組成および高分子化合物の構造に特に限定はない。電解液（すなわち液状の溶媒，電解質塩および添加剤）については上述のとおりである。高分子化合物としては、例えば、ポリアクリロニトリル、ポリフッ化ビニリデン、ポリフッ化ビニリデンとポリヘキサフルオロプロピレンとの共重合体、ポリテトラフルオロエチレン、ポリヘキサフルオロプロピレン、ポリエチレンオキサイド、ポリプロピレンオキサイド、ポリフォスファゼン、ポリシロキサン、ポリ酢酸ビニル、ポリビニルアルコール、ポリメタクリル酸メチル、ポリアクリル酸、ポリメタクリル酸、スチレン−ブタジエンゴム、ニトリル−ブタジエンゴム、ポリスチレンあるいはポリカーボネートが挙げられる。特に、電気化学的安定性の点からは、ポリアクリロニトリル、ポリフッ化ビニリデン、ポリヘキサフルオロプロピレンあるいはポリエチレンオキサイドの構造を持つ高分子化合物を用いることが望ましい。電解液に対する高分子化合物の添加量は、両者の相溶性によっても異なるが、通常、電解液の５質量％〜５０質量％に相当する高分子化合物を添加することが好ましい。
【００５６】
また、リチウム塩の含有量は、電解液の場合と同様である。但し、ここで溶媒というのは、液状の溶媒のみを意味するのではなく、電解質塩を解離させることができ、イオン伝導性を有するものを広く含む概念である。よって、高分子化合物にイオン伝導性を有するものを用いる場合には、その高分子化合物も溶媒に含まれる。
【００５７】
この二次電池は、例えば、次のようにして製造することができる。
【００５８】
まず、例えば、リチウムを吸蔵・離脱可能な正極材料と、導電剤と、結着剤とを混合して正極合剤を調製し、この正極合剤をＮ−メチル−２−ピロリドンなどの溶剤に分散してペースト状の正極合剤スラリーとする。この正極合剤スラリーを正極集電体２１ａに塗布し溶剤を乾燥させたのち、ロールプレス機などにより圧縮成型して正極合剤層２１ｂを形成し、正極２１を作製する。
【００５９】
次いで、例えば、リチウムを吸蔵・離脱可能な負極材料と、結着剤とを混合して負極合剤を調製し、この負極合剤をＮ−メチル−２−ピロリドンなどの溶剤に分散してペースト状の負極合剤スラリーとする。この負極合剤スラリーを負極集電体２２ａに塗布し溶剤を乾燥させたのち、ロールプレス機などにより圧縮成型して負極合剤層２２ｂを形成し、負極２２を作製する。
【００６０】
続いて、正極集電体２１ａに正極リード２５を溶接などにより取り付けると共に、負極集電体２２ａに負極リード２６を溶接などにより取り付ける。そののち、正極２１と負極２２とをセパレータ２３を介して巻回し、正極リード２５の先端部を安全弁機構１５に溶接すると共に、負極リード２６の先端部を電池缶１１に溶接して、巻回した正極２１および負極２２を一対の絶縁板１２，１３で挟み電池缶１１の内部に収納する。正極２１および負極２２を電池缶１１の内部に収納したのち、電解質を電池缶１１の内部に注入し、セパレータ２３に含浸させる。そののち、電池缶１１の開口端部に電池蓋１４，安全弁機構１５および熱感抵抗素子１６をガスケット１７を介してかしめることにより固定する。これにより、図１に示した二次電池が形成される。
【００６１】
この二次電池は次のように作用する。
【００６２】
この二次電池では、充電を行うと、正極合剤層２１ｂからリチウムイオンが離脱し、セパレータ２３に含浸された電解質を介して、まず、負極合剤層２２ｂに含まれるリチウムを吸蔵・離脱可能な負極材料に吸蔵される。更に充電を続けると、開回路電圧が過充電電圧よりも低い状態において、充電容量がリチウムを吸蔵・離脱可能な負極材料の充電容量能力を超え、リチウムを吸蔵・離脱可能な負極材料の表面にリチウム金属が析出し始める。そののち、充電を終了するまで負極２２にはリチウム金属が析出し続ける。これにより、負極合剤層２２ｂの外観は、例えばリチウムを吸蔵・離脱可能な負極材料として黒鉛を用いる場合、黒色から黄金色、更には白銀色へと変化する。
【００６３】
次いで、放電を行うと、まず、負極２２に析出したリチウム金属がイオンとなって溶出し、セパレータ２３に含浸された電解質を介して、正極合剤層２１ｂに吸蔵される。更に放電を続けると、負極合剤層２２ｂ中のリチウムを吸蔵・離脱可能な負極材料に吸蔵されたリチウムイオンが離脱し、電解質を介して正極合剤層２１ｂに吸蔵される。よって、この二次電池では、従来のいわゆるリチウム二次電池およびリチウムイオン二次電池の両方の特性、すなわち高いエネルギー密度および良好な充放電サイクル特性が得られる。
【００６４】
特に本実施の形態では、電解質がＭ−Ｏ結合を有するリチウム塩を含有しているので、充放電サイクル中に負極２２の表面に安定した被膜が形成されるものと考えられる。これにより、負極２２における溶媒の分解反応が抑制されると共に、負極２２において析出したリチウム金属と溶媒との反応が防止される。よって、リチウム金属の析出・溶解効率が向上する。
【００６５】
このように本実施の形態によれば、電解質がＭ−Ｏ結合を有するリチウム塩を含有するようにしたので、負極２２における溶媒の分解反応を抑制することができると共に、負極２２において析出したリチウム金属と溶媒との反応を防止することができる。よって、リチウム金属の析出・溶解効率を向上させることができ、サイクル特性などの電池特性を向上させることができる。
【００６６】
特に、Ｍ−Ｏ結合を有するリチウム塩に加えて、他のリチウム塩を含有するようにすれば、保存特性などの電池特性を向上させることができる。
【００６７】
【実施例】
更に、本発明の具体的な実施例について、図１および図２を参照して詳細に説明する。
【００６８】
（実施例１〜６）
正極２１と負極２２との面積密度比を調製し、負極２２の容量が、リチウムの吸蔵および離脱による容量成分と、リチウムの析出および溶解による容量成分とを含み、かつその和により表される電池を作製した。
【００６９】
まず、炭酸リチウム（Ｌｉ₂ ＣＯ₃ ）と炭酸コバルト（ＣｏＣＯ₃ ）とを、Ｌｉ₂ ＣＯ₃ ：ＣｏＣＯ₃ ＝０．５：１（モル比）の割合で混合し、空気中において９００℃で５時間焼成して、正極材料としてのリチウム・コバルト複合酸化物（ＬｉＣｏＯ₂ ）を得た。次いで、このリチウム・コバルト複合酸化物９１質量部と、導電剤であるグラファイト６質量部と、結着剤であるポリフッ化ビニリデン３質量部とを混合して正極合剤を調整した。続いて、この正極合剤を溶剤であるＮ−メチル−２−ピロリドンに分散して正極合剤スラリーとし、厚み２０μｍの帯状アルミニウム箔よりなる正極集電体２１ａの両面に均一に塗布して乾燥させ、ロールプレス機で圧縮成型して正極合剤層２１ｂを形成し正極２１を作製した。そののち、正極集電体２１ａの一端にアルミニウム製の正極リード２５を取り付けた。
【００７０】
また、負極材料として人造黒鉛粉末を用意し、この人造黒鉛粉末９０質量部と、結着剤であるポリフッ化ビニリデン１０質量部とを混合して負極合剤を調整した。次いで、この負極合剤を溶剤であるＮ−メチル−２−ピロリドンに分散して負極合剤スラリーとしたのち、厚み１５μｍの帯状銅箔よりなる負極集電体２２ａの両面に均一に塗布して乾燥させ、ロールプレス機で圧縮成型して負極合剤層２２ｂを形成し負極２２を作製した。続いて、負極集電体２２ａの一端にニッケル製の負極リード２６を取り付けた。
【００７１】
正極２１および負極２２をそれぞれ作製したのち、厚み２５μｍの微孔性ポリプロピレンフィルムよりなるセパレータ２３を用意し、負極２２，セパレータ２３，正極２１，セパレータ２３の順に積層してこの積層体を渦巻状に多数回巻回し、巻回電極体２０を作製した。
【００７２】
巻回電極体２０を作製したのち、巻回電極体２０を一対の絶縁板１２，１３で挟み、負極リード２６を電池缶１１に溶接すると共に、正極リード２５を安全弁機構１５に溶接して、巻回電極体２０をニッケルめっきした鉄製の電池缶１１の内部に収納した。そののち、電池缶１１の内部に電解液を減圧方式により注入した。電解液には、炭酸エチレン５０体積％と炭酸ジエチル５０体積％とを混合した溶媒に、電解質塩としてリチウム塩を溶解させたものを用いた。
【００７３】
その際、実施例１〜６で、リチウム塩の種類および含有量を表１に示したように変化させた。このうち実施例１は化３に示したリチウムビス［１，２−ベンゼンジオラト（２−）−Ｏ，Ｏ’］ボレートを用いたものであり、実施例２〜５は化３に示したリチウムビス［１，２−ベンゼンジオラト（２−）−Ｏ，Ｏ’］ボレートと他のリチウム塩とを混合して用いたものであり、実施例６は化４に示したリチウムトリス［１，２−ベンゼンジオラト（２−）−Ｏ，Ｏ’］フォスフェートを用いたものである。電解質塩の含有量は、実施例１〜６のいずれについても、０．５ｍｏｌ／ｌとした。
【００７４】
【表１】

【００７５】
電池缶１１の内部に電解液を注入したのち、表面にアスファルトを塗布したガスケット１７を介して電池蓋１４を電池缶１１にかしめることにより、実施例１〜６について直径１４ｍｍ、高さ６５ｍｍの円筒型二次電池を得た。
【００７６】
また、本実施例に対する比較例１として、電解質塩としてＬｉＰＦ₆ を用いたことを除き、他は本実施例と同様にして二次電池を作製した。更に、本実施例に対する比較例２，３として、正極と負極との面積密度比を調製し、負極の容量がリチウムの吸蔵および離脱により表されるリチウムイオン二次電池を作製した。その際、比較例２では電解質塩として実施例２と同様に化３のリチウム塩とＬｉＰＦ₆ とを用い、比較例３では電解質塩としてＬｉＰＦ₆ を用いた。
【００７７】
得られた実施例１〜６および比較例１〜３の二次電池について、サイクル特性および保存特性をそれぞれ調べた。サイクル特性としては、常温で充放電試験を行い、初回容量（１サイクル目の容量）に対する１００サイクル目の容量維持率（１００サイクル目の容量／初回容量）×１００を求めた。その際、充電は、６００ｍＡの定電流で電池電圧が４．２Ｖに達するまで行ったのち、４．２Ｖの定電圧で電流が１ｍＡに達するまで行い、放電は、４００ｍＡの定電流で電池電圧が３．０Ｖに達するまで行った。ちなみに、ここに示した条件で充放電を行えば、完全充電状態および完全放電状態となる。得られた結果を表１に示す。
【００７８】
なお、実施例１〜６および比較例１〜３の二次電池について、上述した条件で１サイクル充放電を行ったのち再度完全充電させたものを解体し、目視および ⁷Ｌｉ核磁気共鳴分光法により、負極合剤層２２ｂにリチウム金属が析出しているか否かを調べた。更に、上述した条件で２サイクル充放電を行い、完全放電させたものを解体し、同様にして、負極合剤層２２ｂにリチウム金属が析出しているか否かを調べた。
【００７９】
その結果、実施例１〜６および比較例１の二次電池では、完全充電状態においては負極合剤層２２ｂにリチウム金属の存在が認められ、完全放電状態においてはリチウム金属の存在が認められなかった。すなわち、負極２２の容量は、リチウム金属の析出・溶解による容量成分とリチウムの吸蔵・離脱による容量成分とを含み、その和により表されることが確認された。表１にはその結果としてリチウム金属の析出有りとして記載した。
【００８０】
一方、比較例２，３の二次電池では、完全充電状態においても完全放電状態においてもリチウム金属の存在は認められず、リチウムイオンの存在が認められたのみであった。また、完全放電状態において認められたリチウムイオンに帰属するピークはごく小さいものであった。すなわち、負極の容量は、リチウムの吸蔵・離脱による容量成分により表されることが確認された。表１にはその結果としてリチウム金属の析出無しと記載した。
【００８１】
また、保存特性としては、上述した条件で２サイクル目の充電を行い、６０℃の恒温槽中に２週間保存した後、上述した条件で放電を行い、初回容量に対する保存後の容量維持率（保存後の容量／初回容量）×１００を求めた。得られた結果を表１に示す。
【００８２】
表１から分かるように、Ｍ−Ｏ結合を有するリチウム塩を用いた実施例１〜６によれば、用いていない比較例１に比べて、１００サイクル目の容量維持率を高くすることができた。これに対して、リチウムイオン二次電池である比較例２，３では、Ｍ−Ｏ結合を有するリチウム塩を用いた比較例２の方が、用いていない比較例３よりもサイクル特性が低かった。
【００８３】
また、負極２２の容量が、軽金属の吸蔵および離脱による容量成分と、軽金属の析出および溶解による容量成分とを含み、かつその和により表される実施例１〜６では、初回容量が１０６０ｍＡｈ以上であるのに対して、リチウムイオン二次電池である比較例２，３では、９００ｍＡｈ程度であった。
【００８４】
すなわち、負極２２の容量が、軽金属の吸蔵および離脱による容量成分と、軽金属の析出および溶解による容量成分とを含み、かつその和により表される二次電池において、電解液がＭ−Ｏ結合を有するリチウム塩を含有するようにすれば、大きな容量を得ることができ、かつ充放電サイクル特性を向上させることができることが分かった。
【００８５】
更に、実施例１〜５を比較すれば分かるように、化３のリチウム塩と他のリチウム塩とを混合して用いた実施例２〜５によれば、化３のリチウム塩のみを用いた実施例１に比べて、保存後の容量維持率を高くすることができた。すなわち、Ｍ−Ｏ結合を有するリチウム塩に加えて、他のリチウム塩を混合して用いるようにすれば、保存特性を向上させることができることが分かった。
【００８６】
なお、上記実施例では、Ｍ−Ｏ結合を有するリチウム塩について具体的に例を挙げて説明したが、上述した効果はＭ−Ｏ結合に起因するものと考えられる。よって、Ｍ−Ｏ結合を有する他のリチウム塩を用いても同様の結果を得ることができる。また、上記実施例では、電解液を用いる場合について説明したが、ゲル状の電解質を用いても同様の結果を得ることができる。
【００８７】
以上、実施の形態および実施例を挙げて本発明を説明したが、本発明は上記実施の形態および実施例に限定されるものではなく、種々変形可能である。例えば、上記実施の形態および実施例においては、軽金属としてリチウムを用いる場合について説明したが、ナトリウム（Ｎａ）あるいはカリウム（Ｋ）などの他のアルカリ金属、またはマグネシウムあるいはカルシウム（Ｃａ）などのアルカリ土類金属、またはアルミニウムなどの他の軽金属、またはリチウムあるいはこれらの合金を用いる場合についても、本発明を適用することができ、同様の効果を得ることができる。その際、軽金属を吸蔵および離脱することが可能な負極材料、正極材料、非水溶媒、あるいは電解質塩などは、その軽金属に応じて選択される。すなわち、上記実施の形態および実施例では、電解質塩として、Ｍ−Ｏ結合を有するリチウム塩を用いるようにしたが、その軽金属に応じたＭ−Ｏ結合を有する軽金属塩が用いられる。
【００８８】
但し、軽金属としてリチウムまたはリチウムを含む合金を用いるようにすれば、現在実用化されているリチウムイオン二次電池との電圧互換性が高いので好ましい。なお、軽金属としてリチウムを含む合金を用いる場合には、電解質中にリチウムと合金を形成可能な物質が存在し、析出の際に合金を形成してもよく、また、負極にリチウムと合金を形成可能な物質が存在し、析出の際に合金を形成してもよい。
【００８９】
また、上記実施の形態および実施例においては、電解液または固体状の電解質の１種であるゲル状の電解質を用いる場合について説明したが、他の電解質を用いるようにしてもよい。他の電解質としては、例えば、イオン伝導性を有する高分子化合物に電解質塩を分散させた有機固体電解質、イオン伝導性セラミックス，イオン伝導性ガラスあるいはイオン性結晶などよりなる無機固体電解質、またはこれらの無機固体電解質と電解液とを混合したもの、またはこれらの無機固体電解質とゲル状の電解質あるいは有機固体電解質とを混合したものが挙げられる。
【００９０】
更に、上記実施の形態および実施例においては、巻回構造を有する円筒型の二次電池について説明したが、本発明は、巻回構造を有する楕円型あるいは多角形型の二次電池、または正極および負極を折り畳んだりあるいは積み重ねた構造を有する二次電池についても同様に適用することができる。加えて、いわゆるコイン型，ボタン型あるいは角型などの二次電池についても適用することができる。また、二次電池に限らず、一次電池についても適用することができる。
【００９１】
【発明の効果】
以上説明したように請求項１ないし請求１２のいずれか１項に記載の電池によれば、電解質がＭ−Ｏ結合を有する軽金属塩を含有するようにしたので、負極における電解質の分解反応を抑制することができると共に、負極に析出した軽金属と電解質との反応を防止することができる。よって、軽金属の析出・溶解効率を向上させることができ、サイクル特性などの電池特性を向上させることができる。また、電解質がＭ−Ｏ結合を有する軽金属塩に加えて、他の軽金属塩を含有するようにしたので、保存特性などの電池特性を向上させることができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る二次電池の構成を表す断面図である。
【図２】図１に示した二次電池における巻回電極体の一部を拡大して表す断面図である。
【符号の説明】
１１…電池缶、１２，１３…絶縁板、１４…電池蓋、１５…安全弁機構、１５ａ…ディスク板、１６…熱感抵抗素子、１７…ガスケット、２０…巻回電極体、２１…正極、２１ａ…正極集電体、２１ｂ…正極合剤層、２２…負極、２２ａ…負極集電体、２２ｂ…負極合剤層、２３…セパレータ、２４…センターピン、２５…正極リード、２６…負極リード[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery including an electrolyte together with a positive electrode and a negative electrode, and in particular, the capacity of the negative electrode includes a capacity component due to insertion and extraction of light metals and a capacity component due to precipitation and dissolution of light metals, and is expressed by the sum thereof. Related to the battery.
[0002]
[Prior art]
In recent years, mobile electronic devices such as mobile phones, PDAs (personal digital assistants) or notebook computers have been energetically reduced in size and weight, and as part of these efforts, Improvement of the energy density of a battery as a driving power source, particularly a secondary battery is strongly desired.
[0003]
As a secondary battery capable of obtaining a high energy density, for example, there is a lithium ion secondary battery using a material capable of inserting and extracting lithium (Li) such as a carbon material in a negative electrode. In the lithium ion secondary battery, since the lithium occluded in the negative electrode material is designed to be in an ionic state, the energy density greatly depends on the number of lithium ions that can be occluded in the negative electrode material. Therefore, in the lithium ion secondary battery, it is considered that the energy density can be further improved by increasing the amount of occlusion of lithium ions. However, the storage capacity of graphite, which is the material that can store and release lithium ions most efficiently at present, is theoretically limited to 372 mAh in terms of the amount of electricity per gram. Development activities are raising the limit.
[0004]
As a secondary battery capable of obtaining a high energy density, there is a lithium secondary battery that uses lithium metal for the negative electrode and uses only precipitation and dissolution reactions of lithium metal for the negative electrode reaction. The lithium secondary battery has a lithium metal theoretical electrochemical equivalent of 2054 mAh / cm.^ThreeSince it corresponds to 2.5 times the graphite used in lithium ion secondary batteries, it is expected that a higher energy density than that of lithium ion secondary batteries can be obtained. Until now, many researchers have made research and development on practical application of lithium secondary batteries (for example, Lithium Batteries, edited by Jean-Paul Gabano, Academic Press, 1983, London, New York).
[0005]
However, the lithium secondary battery has a problem that it is difficult to put into practical use because the discharge capacity is greatly deteriorated when charging and discharging are repeated. This capacity deterioration is based on the fact that the lithium secondary battery uses the precipitation and dissolution reaction of lithium metal in the negative electrode, and the volume of the negative electrode corresponds to the lithium ions that move between the positive and negative electrodes with charge and discharge. This is due to the fact that the volume of the negative electrode changes greatly, and the dissolution reaction and recrystallization reaction of the lithium metal crystal are difficult to proceed reversibly. In addition, the volume change of the negative electrode becomes so large as to achieve a high energy density, and the capacity deterioration becomes more remarkable.
[0006]
Accordingly, the present inventors have newly developed a secondary battery in which the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium, and is expressed by the sum thereof (International (See published WO 01/22519 A1 pamphlet). In this method, a carbon material capable of inserting and extracting lithium is used for the negative electrode, and lithium is deposited on the surface of the carbon material during charging. According to this secondary battery, it can be expected to improve the charge / discharge cycle characteristics while achieving a high energy density.
[0007]
[Problems to be solved by the invention]
However, in order to put this secondary battery into practical use, it is necessary to further improve and stabilize its characteristics. To this end, not only electrode materials but also research and development on electrolytes are indispensable. In particular, there has been a problem that the charge / discharge cycle characteristics or the storage characteristics are likely to be deteriorated due to the decomposition reaction of the electrolyte in the negative electrode or the reaction between the deposited lithium metal and the electrolyte.
[0008]
The present invention has been made in view of such problems, and an object thereof is to provide a battery capable of improving battery characteristics such as battery capacity, cycle characteristics, and storage characteristics.
[0009]
[Means for Solving the Problems]
  The battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, the negative electrode includes a negative electrode material capable of occluding and releasing light metals, and the negative circuit has an open circuit voltage higher than an overcharge voltage. In the low state, light metal is deposited, and the capacity of the negative electrode includes a capacity component due to light metal occlusion and release and a capacity component due to light metal precipitation and dissolution, and is represented by the sum thereof.The capacity of the negative electrode obtained when inserting and extracting light metal is smaller than the capacity of the positive electrode, and the maximum deposition capacity of light metal deposited on the negative electrode at the maximum voltage before the open circuit voltage becomes the overcharge voltage is 0.05 to 3.0 times the charge capacity capacity of the negative electrode material capable of occluding and releasingThe electrolyte includes a light metal salt having a MO bond (where M represents boron (B) or phosphorus (P)), and LiPF.₆, LiBF_Four, LiN (CF_ThreeSO₂)₂, LiN (C₂F_FiveSO₂)₂, LiC (CF_ThreeSO₂)_ThreeAnd LiClO_FourContaining at least one member of the group consisting of:
[0010]
In the battery according to the present invention, since the electrolyte contains, for example, a light metal salt having a MO bond, the decomposition reaction of the electrolyte is suppressed, and the reaction between the light metal deposited in the light metal precipitation / dissolution reaction and the electrolyte is suppressed. Is prevented. Therefore, the light metal deposition / dissolution efficiency in the negative electrode is improved, and battery characteristics such as cycle characteristics and storage characteristics are improved.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0012]
FIG. 1 shows a cross-sectional structure of a secondary battery according to an embodiment of the present invention. This secondary battery is a so-called cylindrical type, and a wound electrode body 20 in which a belt-like positive electrode 21 and a negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. have. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.
[0013]
At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14, and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15a is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current, and is made of, for example, barium titanate semiconductor ceramics. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.
[0014]
The wound electrode body 20 is wound around a center pin 24, for example. A positive electrode lead 25 made of aluminum or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.
[0015]
FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode mixture layer 21b is provided on both surfaces of a positive electrode current collector 21a having a pair of opposed surfaces. Although not shown, the positive electrode mixture layer 21b may be provided only on one surface of the positive electrode current collector 21a. The positive electrode current collector 21a has, for example, a thickness of about 5 μm to 50 μm and is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode mixture layer 21b has a thickness of 60 μm to 250 μm, for example, and includes a positive electrode material capable of inserting and extracting lithium, which is a light metal. The thickness of the positive electrode mixture layer 21b is the total thickness when the positive electrode mixture layer 21b is provided on both surfaces of the positive electrode current collector 21a.
[0016]
As the positive electrode material capable of inserting and extracting lithium, for example, lithium-containing compounds such as lithium oxide, lithium sulfide, or an intercalation compound containing lithium are suitable, and a mixture of two or more of these is used. May be. In particular, to increase the energy density, the general formula Li_zMO₂A lithium composite oxide represented by or an intercalation compound containing lithium is preferable. Note that M is preferably one or more transition metals, specifically, at least one of cobalt (Co), nickel, manganese (Mn), iron, aluminum, vanadium (V), and titanium (Ti). preferable. z differs depending on the charge / discharge state of the battery, and is usually a value in the range of 0.05 ≦ z ≦ 1.10. In addition, LiMn having a spinel crystal structure₂O_FourOr LiFePO having an olivine type crystal structure_FourIs preferable because a high energy density can be obtained.
[0017]
Such a positive electrode material is prepared by, for example, mixing lithium carbonate, nitrate, oxide or hydroxide with transition metal carbonate, nitrate, oxide or hydroxide so as to have a desired composition. And then pulverized and then fired at a temperature in the range of 600 ° C. to 1000 ° C. in an oxygen atmosphere.
[0018]
The positive electrode mixture layer 21b also contains, for example, a conductive agent, and may further contain a binder as necessary. Examples of the conductive agent include carbon materials such as graphite, carbon black, and ketjen black, and one or more of them are used in combination. In addition to the carbon material, a metal material or a conductive polymer material may be used as long as it is a conductive material. Examples of the binder include synthetic rubbers such as styrene butadiene rubber, fluorine rubber or ethylene propylene diene rubber, or polymer materials such as polyvinylidene fluoride, and one or more of them are mixed. Used. For example, when the positive electrode 21 and the negative electrode 22 are wound as shown in FIG. 1, it is preferable to use a styrene butadiene rubber or a fluorine rubber having high flexibility as the binder.
[0019]
The negative electrode 22 has, for example, a structure in which a negative electrode mixture layer 22b is provided on both surfaces of a negative electrode current collector 22a having a pair of opposed surfaces. Although not shown, the negative electrode mixture layer 22b may be provided only on one surface of the negative electrode current collector 22a. The negative electrode current collector 22a is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil having good electrochemical stability, electrical conductivity, and mechanical strength. In particular, copper foil is most preferable because it has high electrical conductivity. The thickness of the negative electrode current collector 22a is preferably about 5 μm to 40 μm, for example. If the thickness is less than 5 μm, the mechanical strength is reduced, and the negative electrode current collector 22a is easily torn in the manufacturing process, resulting in a decrease in production efficiency. If the thickness is more than 40 μm, the negative electrode current collector 22a in the battery is reduced. This is because the volume ratio becomes larger than necessary and it is difficult to increase the energy density.
[0020]
The negative electrode mixture layer 22b is configured to include any one or two or more negative electrode materials capable of inserting and extracting lithium, which is a light metal. A binder similar to that described above may be included. The thickness of the negative electrode mixture layer 22b is, for example, 40 μm to 250 μm. This thickness is the total thickness when the negative electrode mixture layer 22b is provided on both surfaces of the negative electrode current collector 22a.
[0021]
In this specification, light metal occlusion / release means that light metal ions are electrochemically occluded / released without losing their ionicity. This includes not only the case where the occluded light metal exists in a complete ionic state but also the case where it exists in a state that cannot be said to be a complete ionic state. As a case corresponding to these, for example, occlusion by an electrochemical intercalation reaction of light metal ions to graphite can be mentioned. Further, light metal occlusion in an alloy containing an intermetallic compound or light metal occlusion by formation of an alloy can also be mentioned.
[0022]
Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials such as graphite, non-graphitizable carbon, and graphitizable carbon. These carbon materials are preferable because the change in crystal structure that occurs during charge / discharge is very small, a high charge / discharge capacity can be obtained, and good charge / discharge cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density.
[0023]
As the graphite, for example, the true density is 2.10 g / cm.^ThreeThe above is preferable, 2.18 g / cm^ThreeThe above is more preferable. In order to obtain such a true density, it is necessary that the (002) plane C-axis crystallite thickness is 14.0 nm or more. Further, the (002) plane spacing is preferably less than 0.340 nm, and more preferably in the range of 0.335 nm to 0.337 nm.
[0024]
The graphite may be natural graphite or artificial graphite. If it is artificial graphite, for example, it can be obtained by carbonizing an organic material, subjecting it to high-temperature heat treatment, and pulverizing and classifying it. For example, nitrogen (N₂), Etc. in an inert gas stream, and the temperature is raised to 900 ° C. to 1500 ° C. at a rate of 1 ° C. to 100 ° C. per minute, and this temperature is maintained for about 0 to 30 hours. While baking, heating is performed at 2000 ° C. or higher, preferably 2500 ° C. or higher, and this temperature is maintained for an appropriate time.
[0025]
  As the organic material to be a starting material, coal or pitch can be used. For pitch, for example, tars obtained by thermally decomposing coal tar, ethylene bottom oil or crude oil at high temperature, asphalt, etc. (vacuum distillation, atmospheric distillation or steam distillation), thermal polycondensation, extraction, What is obtained by chemical polycondensation, wooddry distillationSometimes produced are polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate or 3,5-dimethylphenol resin. These coals or pitches exist as liquids at a maximum temperature of about 400 ° C. during carbonization, and the aromatic rings are condensed and polycyclic by being held at that temperature, and are in a stacked orientation state. It becomes a solid carbon precursor, that is, semi-coke (liquid phase carbonization process).
[0026]
Examples of the organic material include condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphen, and pentacene or derivatives thereof (for example, carboxylic acids, carboxylic anhydrides, and carboxylic acids of the above-described compounds). Imide), or mixtures thereof. Furthermore, condensed heterocyclic compounds such as acenaphthylene, indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine, or a derivative thereof, or a mixture thereof can also be used.
[0027]
The pulverization may be performed either before or after carbonization, calcination, or during the temperature raising process before graphitization. In these cases, heat treatment for graphitization is finally performed in a powder state. However, in order to obtain a graphite powder having a high bulk density and high fracture strength, it is preferable to form a raw material and then perform a heat treatment, and pulverize and classify the obtained graphitized molded body.
[0028]
For example, when producing a graphitized molded body, coke as a filler and a binder pitch as a molding agent or a sintering agent are mixed and molded, and then the molded body is heat-treated at a low temperature of 1000 ° C. or lower. After repeating the firing step and the pitch impregnation step of impregnating the binder pitch melted in the fired body several times, heat treatment is performed at a high temperature. The impregnated binder pitch is carbonized and graphitized in the above heat treatment process. Incidentally, in this case, since filler (coke) and binder pitch are used as raw materials, they are graphitized as polycrystals, and sulfur and nitrogen contained in the raw materials are generated as a gas during heat treatment. A minute hole is formed in the path. Therefore, this vacancy makes it easy for the lithium occlusion / release reaction to proceed, and there is also an advantage that the treatment efficiency is industrially high. In addition, as a raw material of a molded object, you may use the filler which has a moldability and sintering property in itself. In this case, it is not necessary to use a binder pitch.
[0029]
As non-graphitizable carbon, the (002) plane spacing is 0.37 nm or more and the true density is 1.70 g / cm.^ThreeIt is preferable that it is less than or less than 700 ° C. in the differential thermal analysis (DTA) in air.
[0030]
Such non-graphitizable carbon can be obtained, for example, by heat-treating an organic material at about 1200 ° C., and pulverizing and classifying it. In the heat treatment, for example, carbonization is performed at 300 ° C. to 700 ° C. as necessary (solid-phase carbonization process), and then the temperature is raised to 900 ° C. to 1300 ° C. at a rate of 1 ° C. to 100 ° C. per minute. It is performed by holding for about 30 hours. The pulverization may be performed before or after carbonization or during the temperature raising process.
[0031]
As the organic material to be the starting material, for example, furfuryl alcohol or furfural polymer, copolymer, or furan resin that is a copolymer of these polymers and other resins can be used. Crustaceans including phenolic resins, acrylic resins, halogenated vinyl resins, polyimide resins, polyamideimide resins, polyamide resins, conjugated resins such as polyacetylene or polyparaphenylene, cellulose or derivatives thereof, coffee beans, bamboos, and chitosan Also, biocellulose using bacteria can be used. Furthermore, a functional group containing oxygen (O) is introduced into petroleum pitch having a hydrogen atom (H) to carbon atom (C) ratio H / C of, for example, 0.6 to 0.8 (so-called oxygen crosslinking). The compound prepared can also be used.
[0032]
The oxygen content in this compound is preferably 3% or more, and more preferably 5% or more (see Japanese Patent Application Laid-Open No. 3-252053). This is because the oxygen content affects the crystal structure of the carbon material, and the physical properties of the non-graphitizable carbon can be increased and the capacity of the anode 22 can be improved at a content higher than this. Incidentally, petroleum pitch, for example, tar (obtained by pyrolyzing coal tar, ethylene bottom oil or crude oil, etc.) at high temperature, or asphalt is distilled (vacuum distillation, atmospheric distillation or steam distillation), It can be obtained by condensation, extraction or chemical polycondensation. Examples of the method for forming an oxidative bridge include a wet method in which an aqueous solution such as nitric acid, sulfuric acid, hypochlorous acid, or a mixed acid thereof is reacted with petroleum pitch, or an oxidizing gas such as air or oxygen is reacted with petroleum pitch. Or a dry method in which a solid reagent such as sulfur, ammonium nitrate, ammonia persulfate, or ferric chloride is reacted with petroleum pitch.
[0033]
Note that the organic material that is a starting material is not limited to these, and any other organic material may be used as long as it is an organic material that can be converted into non-graphitizable carbon through a solid-phase carbonization process by oxygen crosslinking treatment or the like.
[0034]
As the non-graphitizable carbon, in addition to those produced using the above-mentioned organic materials as starting materials, there are also compounds mainly composed of phosphorus (P), oxygen and carbon described in JP-A-3-137010. Since the physical property parameters described above are shown, it is preferable.
[0035]
Examples of the negative electrode material capable of inserting and extracting lithium include a single element, an alloy, or a compound of a metal element or a metalloid element capable of forming an alloy with lithium. These are preferable because a high energy density can be obtained. In particular, when used together with a carbon material, a high energy density can be obtained and an excellent charge / discharge cycle characteristic can be obtained. Note that in this specification, alloys include those composed of one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. The structures include solid solutions, eutectics (eutectic mixtures), intermetallic compounds, or those in which two or more of them coexist.
[0036]
Examples of such metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), and cadmium. (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium (Hf). It is done. These alloys or compounds include, for example, the chemical formula Ma_sMb_tLi_uOr the chemical formula Ma_pMc_qMd_rThe thing represented by is mentioned. In these chemical formulas, Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, Mb represents at least one of a metal element and a metalloid element other than lithium and Ma, Mc represents at least one of nonmetallic elements, and Md represents at least one of metallic elements and metalloid elements other than Ma. The values of s, t, u, p, q, and r are s> 0, t ≧ 0, u ≧ 0, p> 0, q> 0, and r ≧ 0, respectively.
[0037]
Among these, a single element, alloy or compound of Group 4B metal element or metalloid element is preferable, and silicon or tin, or an alloy or compound thereof is particularly preferable. These may be crystalline or amorphous.
[0038]
Specific examples of such alloys or compounds include LiAl, AlSb, CuMgSb, SiB_Four, SiB₆, Mg₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu_FiveSi, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si_ThreeN_Four, Si₂N₂O, SiO_v(0 <v ≦ 2), SnO_w(0 <w ≦ 2), SnSiO_Three, LiSiO or LiSnO.
[0039]
Examples of the negative electrode material capable of inserting and extracting lithium further include other metal compounds or polymer materials. Other metal compounds include oxides such as iron oxide, ruthenium oxide and molybdenum oxide, or LiN_ThreeExamples of the polymer material include polyacetylene, polyaniline, and polypyrrole.
[0040]
Further, in this secondary battery, lithium metal starts to deposit on the negative electrode 22 when the open circuit voltage (that is, the battery voltage) is lower than the overcharge voltage during the charging process. That is, lithium metal is deposited on the negative electrode 22 in a state where the open circuit voltage is lower than the overcharge voltage, and the capacity of the negative electrode 22 includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium metal. And is expressed as its sum. Therefore, in this secondary battery, both the negative electrode material capable of inserting and extracting lithium and lithium metal function as a negative electrode active material, and the negative electrode material capable of inserting and extracting lithium is a base material on which lithium metal is deposited. It has become.
[0041]
The overcharge voltage refers to the open circuit voltage when the battery is overcharged. For example, the “lithium secondary battery” is one of the guidelines established by the Japan Storage Battery Industry Association (Battery Industry Association). Refers to a voltage that is higher than the open circuit voltage of a “fully charged” battery as defined and defined in the “Safety Evaluation Criteria Guidelines” (SBA G1101). In other words, it refers to a voltage higher than the open circuit voltage after charging using the charging method, standard charging method, or recommended charging method used when determining the nominal capacity of each battery. Specifically, in this secondary battery, for example, the battery is fully charged when the open circuit voltage is 4.2 V, and the negative electrode is capable of inserting and extracting lithium in a part of the open circuit voltage in the range of 0 V to 4.2 V. Lithium metal is deposited on the surface of the material.
[0042]
Thereby, in this secondary battery, it is possible to obtain a high energy density and to improve cycle characteristics and quick charge characteristics. This is the same as the conventional lithium secondary battery using lithium metal or a lithium alloy as a negative electrode in that lithium metal is deposited on the negative electrode 22, but the lithium metal is deposited on a negative electrode material capable of inserting and extracting lithium. It is considered that this is because the following advantages arise.
[0043]
First, it is difficult to deposit lithium metal uniformly in a conventional lithium secondary battery, which causes deterioration of cycle characteristics. However, a negative electrode material capable of occluding and releasing lithium generally has a surface area. Therefore, in this secondary battery, lithium metal can be deposited uniformly. Secondly, in the conventional lithium secondary battery, the volume change accompanying the precipitation / dissolution of lithium metal is large, which causes the cycle characteristics to deteriorate, but in this secondary battery, lithium can be occluded / released. Lithium metal is also deposited in the gaps between the particles of the negative electrode material, so that the volume change is small. Thirdly, in the conventional lithium secondary battery, the larger the amount of lithium metal deposited / dissolved, the greater the above problem. However, in this secondary battery, the insertion / extraction of lithium by an anode material capable of occluding and releasing lithium. Since detachment also contributes to the charge / discharge capacity, the amount of lithium metal deposited / dissolved is small when the battery capacity is large. Fourthly, in a conventional lithium secondary battery, if rapid charging is performed, lithium metal is deposited more unevenly, resulting in further deterioration in cycle characteristics. However, in this secondary battery, lithium is occluded in the initial stage of charging. -Lithium is occluded in the detachable negative electrode material, so that rapid charging becomes possible.
[0044]
In order to obtain these advantages more effectively, for example, the maximum deposition capacity of the lithium metal deposited on the negative electrode 22 at the maximum voltage before the open circuit voltage becomes the overcharge voltage can absorb and desorb lithium. It is preferably 0.05 times or more and 3.0 times or less of the charge capacity capacity of the negative electrode material. This is because when the amount of deposited lithium metal is too large, the same problem as that of the conventional lithium secondary battery occurs, and when the amount is too small, the charge / discharge capacity cannot be sufficiently increased. For example, the discharge capacity capability of the negative electrode material capable of inserting and extracting lithium is preferably 150 mAh / g or more. This is because the larger the lithium occlusion / release ability, the smaller the amount of lithium metal deposited. The charge capacity capability of the negative electrode material can be obtained, for example, from the amount of electricity when a negative electrode using lithium metal as a counter electrode and the negative electrode material as a negative electrode active material is charged to 0 V by a constant current / constant voltage method. The discharge capacity capability of the negative electrode material can be determined from, for example, the amount of electricity when the current is discharged to 2.5 V over 10 hours by the constant current method.
[0045]
The separator 23 is made of, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramic, and has a structure in which two or more kinds of porous films are laminated. May be. Among these, a porous film made of polyolefin is preferable because it is excellent in short-circuit preventing effect and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable as a material constituting the separator 23 because a shutdown effect can be obtained within a range of 100 ° C. or higher and 160 ° C. or lower and the electrochemical stability is excellent. Polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.
[0046]
The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. This electrolytic solution contains a liquid solvent, for example, a nonaqueous solvent such as an organic solvent, and an electrolyte salt dissolved in the nonaqueous solvent, and may contain various additives as necessary. The liquid non-aqueous solvent is made of, for example, a non-aqueous compound and has an intrinsic viscosity at 25 ° C. of 10.0 mPa · s or less. In addition, the intrinsic viscosity in a state where the electrolyte salt is dissolved may be 10.0 mPa · s or less. When a solvent is formed by mixing a plurality of types of nonaqueous compounds, the intrinsic viscosity in the mixed state is What is necessary is just 10.0 mPa * s or less.
[0047]
As such a nonaqueous solvent, various conventionally used nonaqueous solvents can be used. Specifically, cyclic carbonates such as propylene carbonate or ethylene carbonate, chain esters such as diethyl carbonate, dimethyl carbonate or ethylmethyl carbonate, or ethers such as γ-butyrolactone, sulfolane, 2-methyltetrahydrofuran or dimethoxyethane Is mentioned. These may be used alone or in combination of two or more. In particular, from the viewpoint of oxidation stability, it is preferable to include a carbonate ester.
[0048]
As the electrolyte salt, it is preferable to use at least one lithium salt having an M—O bond (wherein M represents any of boron, phosphorus, aluminum, gallium, indium, thallium, arsenic, antimony, or bismuth). Such a lithium salt forms a stable film on the surface of the negative electrode 22 during the charge / discharge cycle, suppresses the decomposition reaction of the solvent, and prevents the reaction between the lithium metal deposited on the negative electrode 22 and the solvent. This is because it is considered possible.
[0049]
  Among these, a lithium salt having a B—O bond or a P—O bond is preferable, and a lithium salt having an O—B—O bond or an O—P—O bond is more preferable. This is because a higher effect can be obtained. As such a lithium salt, lithium bis [1,2-benzenediolato (2-)-O, O'] Borate, or lithium tris [1,2-benzenediolato (2-)-O, O'] Cyclic compounds such as phosphate are preferred. This is because the cyclic portion is also considered to be involved in the formation of the film, and a stable film can be obtained.
[0050]
[Chemical 3]

[0051]
[Formula 4]

[0052]
Moreover, it is preferable to mix and use other lithium salt for electrolyte salt in addition to the lithium salt which has such a MO bond. This is because battery characteristics such as storage characteristics can be further improved. Other lithium salts include, for example, LiAsF₆, LiPF₆, LiBF_FourLiClO_Four, LiB (C₆H_Five)_Four, LiCH_ThreeSO_Three, LiCF_ThreeSO_Three, LiN (CF_ThreeSO₂)₂, LiN (C₂F_FiveSO₂)₂, LiN (C_FourF₉SO₂) (CF_ThreeSO₂), LiC (CF_ThreeSO₂)_ThreeLiAlCl_Four, LiSiF₆, LiCl, or LiBr, and any one of these or a mixture of two or more thereof may be used.
[0053]
Among them, LiPF₆, LiBF_FourLiClO_Four, LiN (CF_ThreeSO₂)₂, LiN (C₂F_FiveSO₂)₂And LiC (CF_ThreeSO₂)_ThreeIs preferable because a higher effect can be obtained and a higher conductivity can be obtained.
[0054]
The content (concentration) of the electrolyte salt is preferably in the range of 0.4 mol / l to 3.0 mol / l with respect to the solvent. Outside this range, there is a risk that sufficient battery characteristics may not be obtained due to an extreme decrease in ionic conductivity. Among them, the content of the lithium salt having an M—O bond is preferably in the range of 0.01 mol / l to 2.0 mol / l with respect to the solvent. This is because a higher effect can be obtained within this range.
[0055]
Instead of the electrolytic solution, a gel electrolyte in which an electrolytic solution is held in a polymer compound may be used. The gel electrolyte is not particularly limited as long as the ion conductivity is 1 mS / cm or more at room temperature, and the composition and the structure of the polymer compound are not particularly limited. The electrolyte solution (that is, liquid solvent, electrolyte salt, and additive) is as described above. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and polyhexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, poly Examples thereof include siloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, and polycarbonate. In particular, from the viewpoint of electrochemical stability, it is desirable to use a polymer compound having a polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene or polyethylene oxide structure. The amount of the polymer compound added to the electrolytic solution varies depending on the compatibility between the two, but it is usually preferable to add a polymer compound corresponding to 5% by mass to 50% by mass of the electrolytic solution.
[0056]
  MaTheContain thidium saltAmountThe same as in the case of the electrolytic solution. However, the term “solvent” here means not only a liquid solvent but also a concept that can dissociate the electrolyte salt and has a wide range of ionic conductivity. Therefore, when using what has ion conductivity for a high molecular compound, the high molecular compound is also contained in a solvent.
[0057]
For example, the secondary battery can be manufactured as follows.
[0058]
First, for example, a positive electrode material capable of inserting and extracting lithium, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and this positive electrode mixture is mixed with a solvent such as N-methyl-2-pyrrolidone. Disperse to obtain a paste-like positive electrode mixture slurry. The positive electrode mixture slurry is applied to the positive electrode current collector 21a and the solvent is dried. Then, the positive electrode mixture layer 21b is formed by compression molding using a roll press or the like, and the positive electrode 21 is manufactured.
[0059]
Next, for example, a negative electrode material capable of inserting and extracting lithium and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone and pasted. A negative electrode mixture slurry. After applying this negative electrode mixture slurry to the negative electrode current collector 22a and drying the solvent, the negative electrode mixture layer 22b is formed by compression molding using a roll press or the like, and the negative electrode 22 is manufactured.
[0060]
Subsequently, the positive electrode lead 25 is attached to the positive electrode current collector 21a by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22a by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, an electrolyte is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIG. 1 is formed.
[0061]
This secondary battery operates as follows.
[0062]
In this secondary battery, when charged, lithium ions are released from the positive electrode mixture layer 21b, and first, the lithium contained in the negative electrode mixture layer 22b can be occluded / released through the electrolyte impregnated in the separator 23. Occluded by a negative electrode material. If the battery is further charged, the charge capacity exceeds the charge capacity of the negative electrode material capable of inserting and extracting lithium when the open circuit voltage is lower than the overcharge voltage. Lithium metal begins to precipitate. After that, lithium metal continues to deposit on the negative electrode 22 until charging is completed. As a result, the appearance of the negative electrode mixture layer 22b changes from black to golden and further to white silver when graphite is used as a negative electrode material capable of inserting and extracting lithium, for example.
[0063]
Next, when discharging is performed, first, lithium metal deposited on the negative electrode 22 is eluted as ions, and is inserted in the positive electrode mixture layer 21 b through the electrolyte impregnated in the separator 23. When the discharge is further continued, lithium ions occluded in the negative electrode material capable of occluding and releasing lithium in the negative electrode mixture layer 22b are released and inserted into the positive electrode mixture layer 21b via the electrolyte. Therefore, in this secondary battery, the characteristics of both the conventional so-called lithium secondary battery and lithium ion secondary battery, that is, high energy density and good charge / discharge cycle characteristics can be obtained.
[0064]
In particular, in the present embodiment, since the electrolyte contains a lithium salt having an MO bond, it is considered that a stable coating is formed on the surface of the negative electrode 22 during the charge / discharge cycle. Thereby, the decomposition reaction of the solvent in the negative electrode 22 is suppressed, and the reaction between the lithium metal deposited in the negative electrode 22 and the solvent is prevented. Therefore, the lithium metal deposition / dissolution efficiency is improved.
[0065]
As described above, according to the present embodiment, since the electrolyte contains a lithium salt having an MO bond, the decomposition reaction of the solvent in the negative electrode 22 can be suppressed, and lithium deposited in the negative electrode 22 can be suppressed. The reaction between the metal and the solvent can be prevented. Therefore, lithium metal deposition / dissolution efficiency can be improved, and battery characteristics such as cycle characteristics can be improved.
[0066]
In particular, if other lithium salts are contained in addition to the lithium salt having an MO bond, battery characteristics such as storage characteristics can be improved.
[0067]
【Example】
Furthermore, specific embodiments of the present invention will be described in detail with reference to FIGS.
[0068]
(Examples 1-6)
A battery in which the area density ratio of the positive electrode 21 and the negative electrode 22 is adjusted, and the capacity of the negative electrode 22 includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium, and is represented by the sum thereof Was made.
[0069]
First, lithium carbonate (Li₂CO_Three) And cobalt carbonate (CoCO_Three) And Li₂CO_Three: CoCO_Three= 0.5: 1 (molar ratio), mixed and fired in air at 900 ° C. for 5 hours to form a lithium-cobalt composite oxide (LiCoO) as a positive electrode material₂) Next, 91 parts by mass of this lithium / cobalt composite oxide, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Subsequently, the positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which is uniformly applied to both surfaces of the positive electrode current collector 21a made of a strip-shaped aluminum foil having a thickness of 20 μm and dried. The positive electrode mixture layer 21b was formed by compression molding with a roll press machine, and the positive electrode 21 was produced. After that, an aluminum positive electrode lead 25 was attached to one end of the positive electrode current collector 21a.
[0070]
Further, an artificial graphite powder was prepared as a negative electrode material, and 90 parts by mass of the artificial graphite powder and 10 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture. Next, this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, and then uniformly applied to both surfaces of a negative electrode current collector 22a made of a strip-shaped copper foil having a thickness of 15 μm. The negative electrode 22 was produced by drying and compression molding with a roll press to form the negative electrode mixture layer 22b. Subsequently, a negative electrode lead 26 made of nickel was attached to one end of the negative electrode current collector 22a.
[0071]
After preparing the positive electrode 21 and the negative electrode 22, a separator 23 made of a microporous polypropylene film having a thickness of 25 μm is prepared, and the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 are stacked in this order to form a spiral structure. The wound electrode body 20 was produced by winding a number of times.
[0072]
After producing the wound electrode body 20, the wound electrode body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. The wound electrode body 20 was housed inside a nickel-plated iron battery can 11. After that, an electrolytic solution was injected into the battery can 11 by a reduced pressure method. As the electrolytic solution, a solution obtained by dissolving a lithium salt as an electrolyte salt in a solvent in which 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate were mixed was used.
[0073]
  At that time, in Examples 1 to 6, the type and content of the lithium salt were changed as shown in Table 1. Of these, Example 1 is lithium bis [1,2-benzenediolato (2-)-O, O′] Borate was used, and Examples 2 to 5 show lithium bis [1,2-benzenediolato (2-)-O, O′] Borate and other lithium salt were used in a mixture, and Example 6 was obtained by using lithium tris [1,2-benzenediolato (2-)-O, O′] Using phosphate. The content of the electrolyte salt was 0.5 mol / l in any of Examples 1 to 6.
[0074]
[Table 1]

[0075]
  After injecting the electrolyte into the battery can 11, the battery lid 14 is caulked to the battery can 11 via the gasket 17 whose surface is coated with asphalt.6A cylindrical secondary battery having a diameter of 14 mm and a height of 65 mm was obtained.
[0076]
Further, as Comparative Example 1 for this example, LiPF was used as the electrolyte salt.₆A secondary battery was fabricated in the same manner as in this example except that was used. Further, as Comparative Examples 2 and 3 for this example, the area density ratio between the positive electrode and the negative electrode was adjusted, and a lithium ion secondary battery in which the capacity of the negative electrode was expressed by insertion and extraction of lithium was manufactured. At that time, in Comparative Example 2, as the electrolyte salt, the lithium salt of Chemical Formula 3 and LiPF were used as in Example 2.₆In Comparative Example 3, LiPF was used as the electrolyte salt.₆Was used.
[0077]
For the obtained secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3, the cycle characteristics and the storage characteristics were examined. As the cycle characteristics, a charge / discharge test was performed at room temperature, and a capacity retention rate (capacity at 100th cycle / initial capacity) × 100 with respect to the initial capacity (capacity at the first cycle) × 100 was obtained. At that time, charging is performed until the battery voltage reaches 4.2 V at a constant current of 600 mA, and then until the current reaches 1 mA at a constant voltage of 4.2 V, and discharging is performed at a constant current of 400 mA. This was done until 3.0V was reached. Incidentally, if charging / discharging is performed under the conditions shown here, a fully charged state and a fully discharged state are obtained. The obtained results are shown in Table 1.
[0078]
In addition, about the secondary battery of Examples 1-6 and Comparative Examples 1-3, what was fully charged again after performing 1 cycle charge / discharge on the conditions mentioned above, and visually and⁷Whether or not lithium metal was deposited on the negative electrode mixture layer 22b was examined by Li nuclear magnetic resonance spectroscopy. Furthermore, two cycles of charge and discharge were performed under the conditions described above, and the completely discharged one was disassembled, and similarly, it was examined whether lithium metal was deposited on the negative electrode mixture layer 22b.
[0079]
As a result, in the secondary batteries of Examples 1 to 6 and Comparative Example 1, the presence of lithium metal was observed in the negative electrode mixture layer 22b in the fully charged state, and the presence of lithium metal was not observed in the fully discharged state. It was. That is, it was confirmed that the capacity of the negative electrode 22 includes a capacity component due to precipitation and dissolution of lithium metal and a capacity component due to insertion and extraction of lithium, and is represented by the sum thereof. Table 1 shows that lithium metal was deposited as a result.
[0080]
On the other hand, in the secondary batteries of Comparative Examples 2 and 3, the presence of lithium metal was not observed in both the fully charged state and the fully discharged state, and only the presence of lithium ions was recognized. Moreover, the peak attributed to the lithium ion observed in the complete discharge state was very small. That is, it was confirmed that the capacity of the negative electrode is represented by a capacity component due to insertion and extraction of lithium. Table 1 shows no lithium metal precipitation as a result.
[0081]
In addition, as the storage characteristics, the second cycle charge is performed under the above-described conditions, the battery is stored in a constant temperature bath at 60 ° C. for 2 weeks, and then discharged under the above-described conditions. Capacity after storage / initial capacity) × 100 was determined. The obtained results are shown in Table 1.
[0082]
As can be seen from Table 1, according to Examples 1 to 6 using a lithium salt having an M—O bond, the capacity retention rate at the 100th cycle can be increased as compared with Comparative Example 1 that is not used. It was. On the other hand, in Comparative Examples 2 and 3 which are lithium ion secondary batteries, Comparative Example 2 using a lithium salt having an MO bond has lower cycle characteristics than Comparative Example 3 which is not used. .
[0083]
Further, in Examples 1 to 6 in which the capacity of the negative electrode 22 includes a capacity component due to insertion and extraction of light metals and a capacity component due to precipitation and dissolution of light metals, and is expressed by the sum thereof, the initial capacity is 1060 mAh or more. On the other hand, in Comparative Examples 2 and 3 which are lithium ion secondary batteries, it was about 900 mAh.
[0084]
That is, in the secondary battery in which the capacity of the negative electrode 22 includes a capacity component due to light metal occlusion and desorption and a capacity component due to light metal precipitation and dissolution, and is expressed by the sum thereof, the electrolyte solution has an MO bond. It has been found that if the lithium salt is contained, a large capacity can be obtained and charge / discharge cycle characteristics can be improved.
[0085]
Further, as can be seen by comparing Examples 1 to 5, according to Examples 2 to 5 in which the lithium salt of Chemical Formula 3 was mixed with another lithium salt, only the lithium salt of Chemical Formula 3 was used. Compared to Example 1, the capacity retention rate after storage could be increased. That is, it was found that the storage characteristics can be improved by mixing and using other lithium salts in addition to the lithium salt having an MO bond.
[0086]
In the above-described examples, the lithium salt having an M—O bond has been described with a specific example. However, the above-described effects are considered to be caused by the M—O bond. Therefore, similar results can be obtained even when other lithium salts having an M—O bond are used. Moreover, although the case where the electrolytic solution is used has been described in the above embodiment, the same result can be obtained even when a gel electrolyte is used.
[0087]
Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above embodiments and examples, the case where lithium is used as the light metal has been described. However, other alkali metals such as sodium (Na) or potassium (K), or alkaline earth such as magnesium or calcium (Ca). The present invention can also be applied to the case where a similar metal, other light metal such as aluminum, lithium, or an alloy thereof is used, and similar effects can be obtained. At that time, a negative electrode material, a positive electrode material, a non-aqueous solvent, an electrolyte salt, or the like capable of inserting and extracting a light metal is selected according to the light metal. That is, in the above-described embodiments and examples, lithium salts having an MO bond are used as the electrolyte salt, but light metal salts having an MO bond corresponding to the light metal are used.
[0088]
However, it is preferable to use lithium or an alloy containing lithium as a light metal because voltage compatibility with a lithium ion secondary battery currently in practical use is high. In addition, when using an alloy containing lithium as a light metal, there is a substance that can form an alloy with lithium in the electrolyte, and the alloy may be formed at the time of precipitation, or an alloy with lithium is formed on the negative electrode. Possible materials are present and may form an alloy during precipitation.
[0089]
Moreover, in the said embodiment and Example, although the case where the gel electrolyte which is 1 type of electrolyte solution or solid electrolyte was used, you may make it use another electrolyte. Other electrolytes include, for example, an organic solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ionic conductivity, an inorganic solid electrolyte made of ionic conductive ceramics, ionic conductive glass, ionic crystals, or the like. Examples include a mixture of an inorganic solid electrolyte and an electrolyte solution, or a mixture of these inorganic solid electrolyte and a gel electrolyte or an organic solid electrolyte.
[0090]
Furthermore, in the above embodiments and examples, a cylindrical secondary battery having a winding structure has been described. However, the present invention can be applied to an elliptical or polygonal secondary battery having a winding structure, or a positive electrode. The present invention can be similarly applied to a secondary battery having a structure in which the negative electrode is folded or stacked. In addition, the present invention can also be applied to a so-called coin type, button type, or square type secondary battery. Moreover, not only a secondary battery but a primary battery is applicable.
[0091]
【The invention's effect】
  As described above, claims 1 to 12According to the battery of any one of the above, since the electrolyte contains a light metal salt having an MO bond, the decomposition reaction of the electrolyte in the negative electrode can be suppressed, and the light metal deposited on the negative electrode And the reaction with the electrolyte can be prevented. Therefore, precipitation / dissolution efficiency of light metal can be improved, and battery characteristics such as cycle characteristics can be improved.Further, since the electrolyte contains other light metal salt in addition to the light metal salt having an MO bond, battery characteristics such as storage characteristics can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the invention.
FIG. 2 is an enlarged cross-sectional view showing a part of a wound electrode body in the secondary battery shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15a ... Disc board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20 ... Winding electrode body, 21 ... Positive electrode, 21a ... positive electrode current collector, 21b ... positive electrode mixture layer, 22 ... negative electrode, 22a ... negative electrode current collector, 22b ... negative electrode mixture layer, 23 ... separator, 24 ... center pin, 25 ... positive electrode lead, 26 ... negative electrode lead

Claims (12)

A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode includes a negative electrode material capable of inserting and extracting light metal, and the negative electrode has light metal deposited in an open circuit voltage lower than an overcharge voltage,
The capacity of the negative electrode includes a capacity component due to insertion and extraction of light metal, and a capacity component due to precipitation and dissolution of light metal, and is represented by the sum thereof.
The capacity of the negative electrode obtained when inserting and extracting light metal is smaller than the capacity of the positive electrode, and the maximum deposition capacity of light metal deposited on the negative electrode at the maximum voltage before the open circuit voltage becomes an overcharge voltage Is 0.05 times or more and 3.0 times or less the charge capacity capability of the negative electrode material capable of inserting and extracting light metals,
The electrolyte includes a light metal salt having a MO bond (where M represents boron (B) or phosphorus (P)), LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ A battery comprising at least one member selected from the group consisting of F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ and LiClO ₄ .   The battery according to claim 1, wherein the light metal salt has a B—O bond or a P—O bond.   The battery according to claim 1, wherein the light metal salt has an O—B—O bond or an O—P—O bond.   The battery according to claim 1, wherein the light metal salt is a cyclic compound. The light metal salt may be lithium bis [1,2-benzenediolato (2-)-O, O ′] borate shown in Chemical Formula 1 or lithium tris [1,2-benzenediolate (2 The battery according to claim 1, wherein the battery is-)-O, O '] phosphate.

  The battery according to claim 1, wherein the negative electrode includes a negative electrode material capable of inserting and extracting light metals.   The battery according to claim 6, wherein the negative electrode contains a carbon material.   The battery according to claim 7, wherein the negative electrode includes at least one selected from the group consisting of graphite, graphitizable carbon, and non-graphitizable carbon.   The battery according to claim 8, wherein the negative electrode contains graphite.   The battery according to claim 6, wherein the negative electrode includes at least one selected from the group consisting of simple elements, alloys and compounds of metal elements or metalloid elements capable of forming an alloy with the light metal.   The negative electrode includes tin (Sn), lead (Pb), aluminum, indium, silicon (Si), zinc (Zn), antimony, bismuth, cadmium (Cd), magnesium (Mg), boron, gallium, and germanium (Ge). 11. The battery according to claim 10, comprising at least one member selected from the group consisting of a simple substance, an alloy, and a compound of nickel, arsenic, silver (Ag), zirconium (Zr), yttrium (Y), or hafnium (Hf). .   The battery according to claim 1, wherein the electrolyte includes a polymer compound or an inorganic solid electrolyte.

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